Authorities also have been interviewing university employees about accounting issues.

The school has acknowledged problems with its accounting procedures. In an e-mail to faculty and staff on Friday, Yale President
Richard Levin
urged employees to cooperate with investigators.

"Regardless of the outcome of the current investigation, we must get all our processes right and make sure that we are good stewards of the funds entrusted to us by the federal government," Levin said in a statement released Monday. "We know that we have more work to do."

The subpoenas cover 47 grants valued at about $45 million, the school said. The university received about $2 billion in grants during the past decade.